feat: add snap-to-grid toggle for track grid regions and playhead

src/components/MainContent.tsx

@@ -13,6 +13,7 @@ import type { RegionUI } from './interfaces';
 import { DEBUG_MODE, BAR_NUMBERS_CONSTANTS } from '../constants';
 import { useRegionOperations } from '../hooks/useRegionOperations';
 import { regionDeleteManager } from '../util/regionDeleteUtil';
+import { KGMainContentState } from '../core/state/KGMainContentState';
 import { ChangeLoopSettingsCommand } from '../core/commands';
 
 interface MainContentProps {
@@ -135,7 +136,7 @@ const MainContent: React.FC<MainContentProps> = ({
         if (region instanceof KGMidiRegion || region instanceof KGAudioRegion) {
           // Calculate bar number and length from beats
           const beatsPerBar = timeSignature.numerator;
-          const barNumber = Math.floor(region.getStartFromBeat() / beatsPerBar) + 1;
+          const barNumber = (region.getStartFromBeat() / beatsPerBar) + 1;
           const length = region.getLength() / beatsPerBar;
 
           // Create a RegionUI object
@@ -517,8 +518,9 @@ const MainContent: React.FC<MainContentProps> = ({
       getComputedStyle(document.documentElement).getPropertyValue('--track-grid-bar-width')
     ) || 40;
 
-    // Find the closest bar start (using Math.round for nearest bar)
-    const barIndex = Math.round(relativeX / barWidth);
+    // Find the closest bar start; honor snapping toggle
+    const snap = KGMainContentState.instance().isSnappingEnabled();
+    const barIndex = snap ? Math.round(relativeX / barWidth) : relativeX / barWidth;
 
     // Ensure we don't go below 0
     const clampedBarIndex = Math.max(0, barIndex);

src/components/Toolbar.tsx

@@ -12,7 +12,7 @@ import {
   FaUndo, FaRedo, FaMousePointer, FaStepBackward,
   FaPlay, FaPause, FaComments, FaSync,
   FaFolderOpen, FaSave, FaDownload, FaUpload, FaPlus,
-  FaCog
+  FaCog, FaMagnet
 } from 'react-icons/fa';
 import { KGProject, type KeySignature } from '../core/KGProject';
 import { plainToInstance } from 'class-transformer';
@@ -48,6 +48,7 @@ const Toolbar: React.FC = () => {
 
   // State for main content tools
   const [activeMainTool, setActiveMainTool] = React.useState<'pointer' | 'pencil'>('pointer');
+  const [isSnapping, setIsSnapping] = React.useState(true);
 
   // State for key signature dropdown
   const [showKeySignatureDropdown, setShowKeySignatureDropdown] = React.useState(false);
@@ -569,6 +570,16 @@ const Toolbar: React.FC = () => {
     }
   };
 
+  // Handle snapping toggle
+  const handleSnappingToggle = () => {
+    const newValue = !isSnapping;
+    setIsSnapping(newValue);
+    KGMainContentState.instance().setSnapping(newValue);
+    if (DEBUG_MODE.TOOLBAR) {
+      console.log(`Snapping ${newValue ? 'enabled' : 'disabled'}`);
+    }
+  };
+
   // Handle copy button click
   const handleCopyClick = () => {
     if (DEBUG_MODE.TOOLBAR) {
@@ -774,13 +785,20 @@ const Toolbar: React.FC = () => {
         >
           <FaMousePointer />
         </button>
-        <button 
-          title="Pencil" 
+        <button
+          title="Pencil"
           className={`tool-button ${activeMainTool === 'pencil' ? 'active' : ''}`}
           onClick={() => handleMainToolSelect('pencil')}
         >
           <FaPencil />
         </button>
+        <button
+          title="Snap to Grid"
+          className={`tool-button ${isSnapping ? 'active' : ''}`}
+          onClick={handleSnappingToggle}
+        >
+          <FaMagnet />
+        </button>
         <div className="toolbar-separator"></div>
         <button title="Copy" onClick={handleCopyClick}><FaCopy /></button>
         <button title="Paste" onClick={handlePasteClick}><FaPaste /></button>

src/components/track/RegionItem.tsx

@@ -307,7 +307,7 @@ const RegionItem: React.FC<RegionItemProps> = ({
     } else {
       renderNotesOnCanvas();
     }
-  }, [midiRegion, audioRegion, audioBuffer, timeSignature, bpm, id, noteUpdateTrigger]);
+  }, [midiRegion, audioRegion, audioBuffer, timeSignature, bpm, id, noteUpdateTrigger, barNumber, length]);
 
   // Re-render canvas when region content size changes
   useEffect(() => {

src/components/track/TrackGridItem.tsx

@@ -268,20 +268,23 @@ const TrackGridItem: React.FC<TrackGridItemProps> = ({
     
     // If the mouse was moved and we have current values, calculate the new values
     if (mouseMoved.current && currentResizeWidth.current !== null && currentResizeLeft.current !== null) {
+      const snap = KGMainContentState.instance().isSnappingEnabled();
+
       if (resizeAction === 'end') {
-        // End resize: round length to nearest bar
-        newLength = Math.max(REGION_CONSTANTS.MIN_REGION_LENGTH, Math.round(currentResizeWidth.current / barWidth));
+        // End resize: snap length to nearest bar, or use raw value
+        const rawLength = currentResizeWidth.current / barWidth;
+        newLength = Math.max(REGION_CONSTANTS.MIN_REGION_LENGTH, snap ? Math.round(rawLength) : rawLength);
       } else if (resizeAction === 'start') {
-        // Start resize: round bar number and adjust length accordingly
+        // Start resize: snap bar number, or use raw value
         const rawBarNumber = currentResizeLeft.current / barWidth + 1;
-        newBarNumber = Math.max(1, Math.round(rawBarNumber));
-        
+        newBarNumber = Math.max(1, snap ? Math.round(rawBarNumber) : rawBarNumber);
+
         // Calculate the difference from the initial position
         const barDiff = initialBarNumberRef.current! - newBarNumber;
-        
+
         // Adjust length to maintain the end position
         newLength = initialLengthRef.current! + barDiff;
-        
+
         // Ensure minimum length
         if (newLength < REGION_CONSTANTS.MIN_REGION_LENGTH) {
           newLength = REGION_CONSTANTS.MIN_REGION_LENGTH;
@@ -434,9 +437,10 @@ const TrackGridItem: React.FC<TrackGridItemProps> = ({
     
     // If the mouse was moved, calculate the final position
     if (mouseMoved.current && currentDragLeft.current !== null && currentDragTop.current !== null) {
-      // Calculate the new bar number and round to nearest integer
+      // Calculate the new bar number; snap to nearest integer when snapping is on
+      const snap = KGMainContentState.instance().isSnappingEnabled();
       const rawBarNumber = (currentDragLeft.current / barWidth) + 1;
-      finalBarNumber = Math.max(1, Math.round(rawBarNumber));
+      finalBarNumber = Math.max(1, snap ? Math.round(rawBarNumber) : rawBarNumber);
       
       // Calculate the closest track based on vertical position
       if (allTracks && allTracks.length > 0 && gridContainerRef.current) {

src/components/track/TrackGridPanel.tsx

@@ -193,6 +193,7 @@ const TrackGridPanel: React.FC<TrackGridPanelProps> = ({
         const secondsPerBeat = 60 / bpm;
         const clipOffset = coreRegion.getClipStartOffsetSeconds();
         const audioDuration = coreRegion.getAudioDurationSeconds();
+        const snap = KGMainContentState.instance().isSnappingEnabled();
 
         // Left edge changed — calculate new clip offset
         if (clampedBarNumber !== oldBarNumber) {
@@ -205,7 +206,9 @@ const TrackGridPanel: React.FC<TrackGridPanelProps> = ({
             // Dragged past audio start — snap to earliest allowed position
             const maxLeftExtensionBeats = clipOffset / secondsPerBeat;
             const minStartBeat = oldStartBeat - maxLeftExtensionBeats;
-            clampedBarNumber = Math.ceil(minStartBeat / beatsPerBar) + 1;
+            clampedBarNumber = snap
+              ? Math.ceil(minStartBeat / beatsPerBar) + 1
+              : (minStartBeat / beatsPerBar) + 1;
             const oldEndBarNumber = oldBarNumber + (coreRegion.getLength() / beatsPerBar);
             clampedLength = oldEndBarNumber - clampedBarNumber;
             newClipStartOffsetSeconds = 0;
@@ -219,7 +222,7 @@ const TrackGridPanel: React.FC<TrackGridPanelProps> = ({
         const maxDurationSeconds = audioDuration - effectiveClipOffset;
         const maxLengthBars = (maxDurationSeconds / secondsPerBeat) / beatsPerBar;
         if (clampedLength > maxLengthBars) {
-          clampedLength = Math.floor(maxLengthBars);
+          clampedLength = snap ? Math.floor(maxLengthBars) : maxLengthBars;
           if (clampedLength < REGION_CONSTANTS.MIN_REGION_LENGTH) {
             clampedLength = REGION_CONSTANTS.MIN_REGION_LENGTH;
           }